The present invention relates to ultrasound cleaning and processing systems, and more particularly, to systems, generators, transducers, circuitry, probes, signals and methods that clean and/or process by coupling sound waves into a liquid. Prior art ultrasound systems lack performance in certain processes such as organism inactivation, cleaning and sonochemistry; and they lack the ability to remove a wide range of particle types and sizes without doing damage to the part being cleaned or processed. This invention improves the performance of an ultrasound system while eliminating the damage causing mechanisms. It also provides consistent performance by monitoring the process and adjusting the ultrasound to compensate for varying process conditions. It further provides highly reliable operation and improved performance at megasonic frequencies.
A primary parameter of ultrasonic performance is frequency, and in particular multiple frequency ultrasound systems. As used herein, “multiple frequency ultrasound systems” will consist of two types, “concurrent multiple ultrasound frequencies” and “successive multiple ultrasound frequencies”.
Concurrent multiple ultrasound frequencies are produced in a liquid filled tank by two or more transducers (or two or more transducer arrays) that couple sound energy into the tank and each of these transducers (or arrays) is driven by a different generator. Typically all the generators are operated at the same time or there is an overlap in the operating times of the generators so that two or more frequencies are simultaneously put into the tank for at least part of the cleaning or processing cycle. The chronological history of concurrent multiple ultrasound frequency equipment starts in 1959 with U.S. Pat. No. 2,891,176 where Branson teaches three transducer arrays driven by three generators, the operation periods of these generators overlap in a way to balance the current in a transformer. In 1974 a tank was designed and built at Branson Cleaning Equipment Company that had an array of 25 kHz transducers on the bottom and a second array of 40 kHz transducers on one side; each of these arrays was simultaneously driven by the appropriate frequency generator. Similar systems were designed and built by others in the 1970's, e.g., Blackstone, but no useful application was found for the technology. In 1981 U.K. Pat. No. 2,097,890A taught three transducer arrays driven by three generators on different phases of a three-phase line. In the mid 1990's Amerimade Technology sold a system consisting of a tank with angled walls and two arrays of transducers on different walls, each array was driven by a different frequency generator, one sweeping around 71.5 kHz and the other sweeping around 104 kHz. At around the same period in time, Zenith sold a two array two generator system operating at 80 kHz and 120 kHz called “crossfire” because the different frequencies intersected at 90 degrees. Unlike the earlier 25 kHz and 40 kHz systems that found no useful application, the personal computer industry now existed and these Amerimade and Zenith systems were sold in large volume to the hard disk drive industry. In U.S. Pat. No. 5,656,095 Honda, et al. teaches high frequency transducers and low frequency transducers on the tank where the high frequency transducers are normally driven and the low frequency transducers are driven for short periods of time to intermittently destroy the high frequency bubbles. In U.S. Pat. Nos. 5,865,199 and 6,019,852 Pedziwatr et al. teaches two arrays of transducers interspersed on the tank and driven by two different frequency generators. In U.S. Pat. No. 5,909,741 Ferrell teaches two arrays of transducers on different angled walls of a plastic container and driven by different frequency generators. In 2004 Crest introduced a three frequency product where the different frequency transducers were spaced in equilateral triangles with each triangle containing the three frequencies and with no frequency next to itself.
These systems have two primary shortcomings; first, the destructive and constructive interference of the different frequency sound waves results in less transient cavitation compared to sweeping single frequency systems with the same total power. Second, the two or more different frequency transducer arrays on a given amount of radiating membrane surface results in lower power at each frequency. In U.S. Pat. Nos. 5,865,199 and 6,019,852 Pedziwatr et al addressed the shortcoming of interference of different frequency sound waves with an interspersed spacing a distance D between adjacent different frequency transducers. D was chosen to enable both sets of transducers to operate simultaneously to transmit the different frequencies. However, workable values of D, for example, 3.2 inches as suggested by Pedziwatr, result in even lower power at each frequency than many prior art systems.
It will be seen that the present invention overcomes the shortcomings of the prior art concurrent ultrasound frequency systems and it results in increased transient cavitation per input watt compared to prior art systems and allows higher power at each frequency than is possible with the Pedziwatr spacing.
Successive ultrasound frequencies are produced when different frequencies are supplied to an ultrasound tank in series, i.e., sweeping frequencies from one frequency range (for example, 38 khz to 42 khz) are followed by sweeping frequencies from a different frequency range (for example, 102 khz to 106 khz). These tanks contain universal transducers that can produce the frequencies in each of the ranges. Successive ultrasound frequencies were supplied in 1998 by Ney Ultrasonics where tanks with four frequency universal transducers were driven by individual, discreet generators operating in frequency ranges around 40 khz, 72 khz, 104 khz and 170 khz. This was the first primitive implementation of supplying different sweeping frequencies in succession to an array of transducers that operated at each of the supplied frequencies, i.e., universal transducers. This equipment used relays to connect the appropriate frequency generator to the array of universal transducers for the period of time required by the process at that frequency. The second frequency required by the process was then supplied to the transducer array by first disconnecting the prior frequency generator and then connecting the generator producing the second sweeping frequency. This frequency switching was done safely by electronic control of the relays and took less than one second of degas time to complete a frequency transition.
One advantage to the use of a single universal transducer array to produce a succession of multiple ultrasound frequencies is the high power density that can be achieved at each frequency. Each frequency utilizes the total membrane surface to supply that frequency as opposed to the necessity of sharing the available real estate among the various frequencies when using discreet frequency transducers. A second advantage for applications requiring transient cavitation is that many cycles of closely spaced frequencies are available to resonate bubbles up to the energy value needed for transient collapse. It can be expect that a process requiring the removal of small particulate contamination, the removal of spores or the high energies required by sonochemistry will be successfully accomplished by this technology.
A third advantage of applying multiple ultrasound frequencies in succession is realized when cleaning delicate parts. For example, components of a computer hard drive, semiconductors, ferrite parts and optical parts can be excited into resonance and fractured by beat frequencies produced by the interaction of two frequencies, such as exist in concurrent multiple ultrasound frequency systems. Synchronized sweeping frequencies in succession prevent this damage. However, it is important that the sweeping frequencies have a non-constant sweep rate to eliminate a second source of resonant damage that exists in many modern day sweeping ultrasonic systems.
The history of applying multiple ultrasound frequencies sequentially starts in 1998 with U.S. Pat. No. 5,834,871 which taught a universal transducer design and driving it from different frequency generators that were selected by a multiplexer. The above described primitive relay system from Ney Ultrasonics was available that same year.
Starting in 1999, follow-on U.S. Pat. Nos. 6,002,195, 6,016,821, 6,181,051 and 6,433,460 disclose improvements on delivering different frequencies in succession to universal transducers and preventing resonant damage to parts being cleaned. In 2000, CAE Ney Ultrasonics replaced the primitive system and sold generators that produced multiple frequencies to drive universal transducers at frequencies selected by a binary code as programmed by a PLC. In 2001 to 2004, U.S. Pat. Nos. 6,313,565; 6,462,461; 6,538,360 and 6,822,372 issued and further protected the multiple ultrasound frequencies in succession technology and the circuitry required to produce these generators. In 2002, Blackstone˜NEY Ultrasonics introduced a seven frequency generator driving universal transducers from 40 kHz to 270 kHz.
Three classes of ultrasonic cleaning and processing equipment exist, the equipment with an operating center frequency in the range of 18 kHz to 100 kHz is normally referred to as ultrasonic equipment, the equipment with an operating center frequency in the range of 100 kHz to 350 kHz is sometimes referred to as microsonic equipment and the equipment with an operating center frequency in the range of 350 kHz to 4 MHz is normally referred to as megasonic equipment. Each different frequency put into a cleaning solution removes a different size and type of contamination with optimum efficiency; therefore, a universal transducer array that could produce one or more frequencies from each of the three frequency ranges is a significant improvement over state of the art equipment.
There is a primary problem to realizing this universal transducer array.
Megasonics transducers do not have a resonance in the ultrasonic and microsonic frequency ranges and therefore cannot be used to produce intense sound waves at these lower frequencies. Ultrasonic or microsonic transducers do not have a useful resonance in the megasonic frequency range and therefore cannot produce intense sound waves at a nominal 1 MHz frequency.
The present invention overcomes the above limitations a wide range multiple frequency transducer array that will economically produce intense sound in the ultrasonic, microsonic and megasonic frequency ranges.
Prior art ultrasound systems also lack performance at megasonic frequencies due to the limitation of one resonant frequency. The present invention overcomes this limitation and teaches improved performance at higher microsonics frequencies and at megasonic frequencies.